The flash memory is still PCIe-based, and remains, thankfully, removable—at least for now. Popping it out for inspection, we find:

Samsung S4LN058A01 PCIe 3.0 x4 AHCI flash controller

Samsung K4E4E324ED 512 MB LPDDR3 DRAM

8 x Samsung K9LDGY8S1D-XCK0 16 GB flash storage (128 GB total)

Apple tells us this bad boy "...features faster flash storage that is up to two times faster than the previous generation."